1. Field of the Invention
The invention relates to adjusting mechanism for the variable nozzle vanes of a gas turbine engine including a unison ring for uniformly varying the nozzle vanes and more particularly to mounting structure for such ring for accomodating dimensional variations in the housing due to thermal changes without effecting the free movement of the unison ring to adjust the vanes.
2. Description of the Prior Art
Unison rings mounted for circumferential movement about the exterior of a turbine housing are well known in the art as a means to couple a row of variable vanes for uniformly changing the angle of the vanes as desired. Heretofore, such unison rings were used to vary the angle of vanes adjacent the inlet to the compressor of a gas turbine engine. In this environment, the unison ring could be supported on rollers mounted directly on the exterior of the housing in that the ambient temperature and the temperature of the casing under running conditions were essentially the same. However, in that area of the casing exposed to the hot motive fluid driving the turbine rotors, the casing expands from its ambient condition, and whereas prior to expansion, the unison ring mounted in the prior art manner would be freely movable, the expansion of the housing without commensurate expansion of the ring (which is separated by a space and thus not exposed to the same temperature) would cause a binding engagement to the end that components might either become overstressed and break or, in the least, the movement of the unison ring would be extremely difficult.